1. Technical Field
The present disclosure relates to a semiconductor package structure and a semiconductor process, and more particularly to a stacked semiconductor package structure and a semiconductor process thereof.
2. Description of the Related Art
A conventional process of making a stacked semiconductor package structure begins with bonding a die and a plurality of solder balls to an upper surface of a lower substrate. Next, a molding process is used to form a molding material on the upper surface of the lower substrate to encapsulate the die and solder balls. Once the molding material is solidified, a high-temperature laser is used to form a plurality of openings on an upper surface of the molding material to expose an upper part of each of the solder balls. Next, an upper substrate is put on the molding material such that a solder on the lower surface of the upper substrate is in contact with the solder balls. At a first heating step, the solder and the solder balls are fused in an oven to make a number of interconnection elements. A reflow process is performed subsequent to the formation of a plurality of solder balls on the lower surface of the lower substrate. A singulation step is performed at the end of the process.
In the conventional manufacturing process, when the semiconductor package structure is moved to the oven, the lower surface of the upper substrate is in contact with, but not bonded to, the molding material, and the solder is in contact with, but not bonded to, the solder balls. Consequently, the upper substrate may move relative to the molding material during the transportation of the semiconductor package structure. Moreover, after the first heating step, the solder on the upper substrate and the solder balls of the lower substrate are bonded together; however, the lower surface of the upper substrate is in contact with, but not bonded to, the molding material. Accordingly, the upper substrate may easily warp after reflow and may even peel off, which adversely affects the reliability of resulting products.
In order to solve the above problems, a solution is provided. The solution is to use solder balls to bond an upper substrate to a lower substrate and then perform a molding process to form a molding material between the upper and lower substrates. Nevertheless, the molding material in such a molding process is injected from a side of the upper and lower substrates into a space between the upper and lower substrates, and the solder balls may affect the flow of the molding material, which may lead to an uneven distribution of the fillers within the molding material. Also, when a liquid state (A-stage) molding material is injected through a mold injection entrance from one side of the upper and lower substrates to the other side of the upper and lower substrates, it can be observed that larger-sized fillers can be conveyed farther than smaller-sized fillers by the liquid state molding material, and, thus, after a curing process (from A-stage to C-stage), the larger-sized fillers can be mostly positioned at the side farther away from the mold injection entrance, and the smaller-sized fillers can be mostly positioned at the side near the mold injection entrance. Moreover, in order to make the molding material pass through a channel between the die and the upper substrate in such a process, solder balls of a predetermined height are used. Accordingly, the reduction of the size of each of the solder balls as well as in the distance between every two of the solder balls is limited.